According to Herbert Casson, in his "The History of the Telephone," the first "exchange for telephone service" used burglar alarm wiring.
"When the first infant exchange for telephone service was born in Boston, in 1877, it was the tiny offspring of a burglar-alarm business operated by E. T. Holmes, a young man whose father had originated the idea of protecting property by electric wires in 1858. Holmes was the first practical man who dared to offer telephone service for sale. He had obtained two telephones, number six and seven, the first five having gone to the junk-heap; and he attached these to a wire in his burglar-alarm office. For two weeks his business friends played with telephones, like boys with a fascinating toy; then Holmes nailed up a new shelf in his office, and on this shelf he placed six box-telephones in a row. These could be switched into connection with the burglar- alarm wires and any two of six wires could be joined by a wire cord. Nothing had been simpler, but it was the arrival of a new idea in the business world."
Herbert N. Casson. "The History of the Telephone." Chicago: A. C. McClurg & Co., 1910, 151-52.
Neal McLain